1. Field of the Invention
The present invention relates generally to methods and apparatus for dispensing liquids and, more particularly, to a method and apparatus for very accurately dispensing a preselected amount of liquid in a drop-by-drop fashion.
2. Description of the Prior Art
It is conventional to employ a metering means, such as a pipette, burette, etc., to transfer small preselected amounts of liquid from a supply container to each of a plurality smaller containers. These types of liquid transfering methods are normally carried out manually to attained the needed accuracy because of the visual measurements required.
However, as the number of preselected amounts increases, it becomes increasing difficult to achieve the desired accuracy because the incidence of human error in measuring increases as the number of measurements per unit time increases. Efforts have been directed at automating the transfer operation, but such efforts have not yielded the desired results of increased accuracy, increased throughout, and lower measurement cost. If the transfer operation could be automated in a satisfactory fashion, it would have applications, for example, in blending and supplying of raw materials, and in blending of catalysts, color formers, sensitizers, etc. SUMMARY OF THE INVENTION
The method and apparatus of the present invention permits a preselected amount of liquid to be very accurately dispensed in a drop-by-drop fashion. The liquid is peristaltically pumped intermittently from a reservoir to a discharge pipe by the successive squeezing and releasing of an elastic tube carrying the liquid and connected to the discharge pipe. The discharge pipe has a discharge port with a face, the face being perpendicular to the longitudinal axis of the discharge pipe. The outer diameter of the discharge pipe at the discharge port is less than or equal to twice the inner diameter of the discharge pipe at the discharge port. The preselected amount of the liquid that is dispensed in a drop-by-drop fashion from the discharge port satisfies the following conditions:
(1) V=Q.times.M.times.C PA1 (2) 50 mg .gtoreq.Q PA1 (3)0.5 seconds .ltoreq.M PA1 (4) 3/seconds .gtoreq.C PA1 (5) 1.5.ltoreq.M.times.C PA1 V is the weight of the produced liquid drop, PA1 Q is the feed quantity of said liquid, PA1 M is the time interval between successive drops, and PA1 C is the cycle of the pump.
wherein: